VAC Signature MK2a pre "phono tube questions"

I have no idea about the particular Chinese 12AX7s that VAC supplies, but don't dismiss them just because they are Chinese. Some of the best 12AT7s I have ever heard were made in China, supplied to me by the Billington company in England. Admittedly, they were "select" types. But they killed Mullards, GE Gold Star 6201s, Philips, and a few others I compared them to. (The Gold Stars took second.)

Good luck finding real NOS Amperex etc.

Hi Lewm,

My preamp arrived and I checked out the VAC 12AX7s. Construction looks identical to my Psvane 12AX7s without the gold plating on the pins. So that means they're almost certainly made by Shugang, which also makes the Psvanes. They're really quite good!

Hello Dev,

You asked me to report back on tube rolling the phono section of my Phi Beta, which has the same circuit as your Sig 2a. I've had it for a week now and I'm ready to make a few preliminary observations after rolling a variety of high-quality 12AX7s, including 1964 Med Grade Amperex (very pricey), mid-'50s RCA long blackplates (one of my favorites), late-'50s Tele ribbed plates, and mid-'60s Lorenz (German-made Amperex). I have several pairs of each and I've tried them in different permutations in the first two positions. Because this circuit is so transparent, all changes in tubes affect the sound quite dramatically. Much to my surprise, however, so far the stock VAC tubes sound best to me. They are very balanced with excellent soundstage and tonality, weight and authority. They just sound "right," perhaps because VAC spends quite a bit of time tuning the sound by ear. I do find myself wanting a tiny bit more extension in the treble, and slightly faster transients, but this is perhaps because my tubes have quite a bit of time on them. I've ordered some Psvanes (I had a pair but wrecked one), which I expect to match this circuit very well since they appear to be of the same manufacture as the stock tubes (Shugang) but at a higher level of quality. I'll report back when I've tried them.

I'll add that I'm extremely impressed with the phono section itself. It's quite a bit better than I was expecting, and holds its own extremely well against my Steelhead II. I'm actually not sure which one I prefer. The Manley (which I've rolled extensively and optimized to my ear) is perhaps more dynamic, with more drive and extension. And it's more flexible in that it allows gain and capacitance adjustment. But the VAC is perhaps a bit more organic and natural. And it has plenty of gain even for a .2 mV cartridge. I could easily live with either, though I'm glad to keep both. Mine is MC/MC. At my request, Brent modified it to allow manual adjustment of impedance loading, unlike the stock Phi Betas, which have user-chosen fixed loading. He built these ingenious screw terminals that allow me to slide in resistors of my choice (I use nude Vishays) so I can really fine-tune the loading for any cartridge. For 100k loading, e.g., I use 10k resistors. It's both extremely flexible and extremely transparent. What a great company! I'm completely in love with this preamp. And you're right, it's a brilliant match with the Bryston 28B-SST2.